In my research of large pendulums for the 10,000 Year Clock I came across the beautifully designed tuned mass damper in the Taipei 101 tower. Basically really tall buildings are themselves massive pendulums, as they are built to sway in the wind and earthquakes. However very tall buildings in earthquake zones need something to dampen this motion.

These mass dampers do that, and are used widely including the ones in the new buildings here in San Francisco that use baffled water tanks. However the one pictured above is the first one I have seen designed with a high degree of aesthetics in mind… It was clearly designed impress people on the building tour. Below is a small animated image of how it counteracts building sway, it pretty much does what you do with your own weight when you are standing on a stool changing that light bulb and it starts to sway.

As pointed out in a couple of the comments there is an astounding video of this mass dampening pendulum in action as the recent earthquakes in China reached the Taipei tower. One guy had the presence of mind to run in and video tape the pendulum in action…

Camron Assadi

Here’s a post with a video of it moving on May 12th, when the earthquake happened in Sichuan, China. Apparently the people in the video ran in to see the ball in action:

Intriguing. Very well done article, highly informative. The video could be better, but it’s amazing as it is. Does the Sears tower in Chicago have a pendulum? My aunt worked there years ago, she said she could often feel the building swaying.

Jim

“it pretty much does what you do with your own weight when you are standing on a stool changing that light bulb and it starts to sway.”

If you’re up that high, stop standing on a stool and get a ladder.

Hono Lulu

Yeah, i’ve seen that before on some other blog. it’s really amazing. wait… i found the link:

really seeing this i was amazed.seeing the way the engineers have put their mind into the making of this huge pendulum i got a sense of respect for them as by making this they will save HUMAN LIFE…………………..THANK you TO ALL THOSE WHO HAVE BUILD THIS “life saving structure.”

If the building is somehow horizontally displaced to certain extent at its top and released freely to move then it will definitely vibrate. But the displacement is to be applied to the building's structural system.

Tuned Mass Dampers, TMD, are the suspended system inside the building's structural system. In earthquakes, TMD starts swinging because it simply won't be participating in building's motion due to its own Inertia. Not due to direct application of any external forces.

Just forcing TMD to swing won't set up whole building in motion as you said mainly because it's just a suspended system; thus no inertial forces would be produced in building's structural system.

No. The building and pendulum are a system. Each dampens the other. They are tuned to dampen each other. It also appears there are pneumatic pistons attached to the pendulum to slow it down. The men would tire long before the pistons!